Random Frustration in two-dimensional spin-1/2 Heisenberg antiferromagnet

Abstract

The square lattice spin-1/2 antiferromagnet containing a dilute concentration, $δ$, of randomly placed ferromagnetic nearest-neighbor bonds is studied at low-temperature via non-linear $σ$-model techniques and by exact diagonalization. We generally find that long-range N\' eel order is destroyed above a critical strength in the defective ferromagnetic exchange coupling-constant given by $|K_c|/J\sim δ^{-1/2}$. We also observe large statistical fluctuations both in the spin-stiffness and in the antiferromagnetic structure-factor near this critical point, suggesting the onset of a spin-glass phase.

13 pgs, TeX, submitted to Phys. Rev. Feb. 22, 1994. (Correct set of figures follow)